Authorities say Glendale Assistant Police Chief Greg Dominguez is the subject of an internal investigation concerning off-duty conduct.
Police officials confirmed the probe Tuesday by the department's Professional Standards Unit.
But they declined to disclose any details, citing a state law which prohibits them from discussing open investigations.
They also won't say what the investigation is focused on.
Dominguez is a 28-year veteran and is one of Glendale's two assistant chiefs. He was promoted to the job in December 2011.